The question of the function or origin of emotional tears remains open. Theories range from the simple, such as response to inflicted pain, to the more complex, including
nonverbal communication in order to elicit
altruistic helping behaviour from others. Some have also claimed that crying can serve several biochemical purposes, such as relieving stress and clearance of the eyes. There is some empirical evidence that crying lowers stress levels, potentially due to the release of hormones such as
oxytocin. Crying is believed to be an outlet or a result of a burst of intense emotional sensations, such as agony, surprise, or joy. This theory could explain why people cry during both cheerful and very painful events. Individuals tend to remember the positive aspects of crying and may link it to other simultaneous positive events, such as resolving feelings of
grief. Together, these features of memory reinforce the idea that crying helped the individual. In
Hippocratic and medieval medicine, tears were associated with the bodily
humors, and crying was seen as purgation of excess humors from the brain.
William James thought of emotions as reflexes prior to rational thought, believing that the physiological response, as if to stress or irritation, is a precondition to cognitively becoming aware of emotions such as fear or anger. William H. Frey II, a biochemist at the
University of Minnesota, proposed that people feel "better" after crying due to the elimination of hormones associated with
stress, specifically
adrenocorticotropic hormone. This, paired with increased mucosal secretion during crying, could support the theory that crying is a mechanism in humans to dispose of this stress hormone when levels become too high. Tears have a limited ability to eliminate chemicals, reducing the likelihood of this theory. Recent psychological theories of crying emphasize the relationship of crying to the experience of perceived helplessness. From this perspective, an underlying experience of helplessness can usually explain why people cry. For example, a person may cry after receiving unexpectedly happy news, ostensibly because they feel powerless or unable to influence what is happening. Emotional tears have also been put into an evolutionary context. One study proposes that crying, by blurring vision, can handicap aggressive or defensive actions and may function as a reliable signal of appeasement, need, or attachment. Oren Hasson, an
evolutionary psychologist in the zoology department at
Tel Aviv University, believes that crying shows vulnerability and submission to an attacker, solicits sympathy and aid from bystanders, and signals shared emotional attachments. Another theory in evolutionary psychology proposed by
Paul D. MacLean is that the vocal component of crying evolved first as a "separation cry" to help reunite parents and offspring. The tears, he speculates, are a result of a link between the development of the
cerebrum and the discovery of fire. MacLean theorizes that since early humans must have
relied heavily on fire, their eyes were frequently producing reflexive tears in response to the smoke. As humans evolved, the smoke may have come to be strongly associated with loss of life and, therefore, sorrow. Many ethologists would disagree. ==Biological response==